Multiplication is a "piece of cake."
It is not hard, it's easy!
The world is your oyster.
You can achieve anything.
Don't let the cat out of the bag.
It means don't tell the secret or don't ruin the surprise.
He is feeling "under the weather."
He feels sick.
She is "catching some Z's."
She is sleeping.
It costs an arm and a leg.
It's expensive.
You can't teach an old dog new tricks.
It's hard for old people to learn something new.
You're pulling my leg.
You're joking.
In hot water.
In trouble.
It slipped my mind.
I forgot.
Break a leg.
Good luck!
You're the "teacher's pet."
The teacher's favorite student.
Don't "throw in the towel!"
Don't give up!
He got up on the wrong side of the bed.
He's grouchy.
It's raining cats and dogs.
It's raining hard.
Hitting the books.
Studying hard.
You can say that again!
I agree!
Let's pig out!
Eat a lot!
Hit the sack.
Go to sleep.
I'm all ears.
I'm listening.
Give it a shot.
Try it.
Hold your horses.
Wait.